1. Field of the Invention
The present invention generally relates to ultrasound imaging. More particularly, the application relates to the generation of 3D images using ultrasound.
2. Discussion of the Related Art
Ultrasound imaging has become a widely used medical imaging modality, due in part to its effectiveness in safely imaging tissue, its ease of use, and lower cost. Ultrasound has become an essential imaging tool in applications such as identifying tissue anomalies, monitoring fetal development, and assisting in guiding surgical devices in invasive treatments.
Considerable effort has recently been devoted to generating 3D images from multiple ultrasound images. By acquiring multiple images of a tissue region of interest, from multiple angles and positions, it is possible to merge the multiple images to generate a 3D image. Approaches to accomplishing this have included (a) precisely measuring the position and orientation of the ultrasound probe for each image acquired; and/or (b) identifying common tissue features across multiple images to serve as markers for registering the plurality of images into a single 3D image space.
Precisely measuring the position and orientation of the ultrasound probe generally requires additional equipment, which is expensive, and complicates the use of the ultrasound probe. For example, one related art approach involves attaching the ultrasound probe to a robotic arm, which precisely controls the position and orientation of the ultrasound probe. Another related art approach involves mounting optical tracking devices to a handheld ultrasound probe. The latter approach requires equipping the room with optical scanning devices, which is expensive to implement and restricts the use of the ultrasound probe to the room in which the optical scanning devices are installed. Further, line-of-sight between the optical scanning devices and the optical tracking devices (mounted on the ultrasound probe) must be maintained in order for the position and orientation of the ultrasound probe to be computed. Both of these related art solutions add considerable cost and complexity to an ultrasound system.
As mentioned above, another approach involves identifying tissue features common to multiple images for registering multiple ultrasound images to a single 3D image space. This is typically done by inferring the relative position and orientation of the ultrasound probe by determining the location of the common tissue features in each ultrasound image. This is generally easier if the ultrasound probe's motion is constrained to the ultrasound image plane, so that the same common features appear in each ultrasound image. In this case, it is generally easy to compute the translation and rotation of the ultrasound probe by computing the displacement of the tissue features between images. However, this is not so simple in the case of out of plane motion. Out of plane motion is that in which the ultrasound probe translates and/or rotates so that tissue features move with a vector component perpendicular to the ultrasound image plane. In this case, tissue features, which are typically required to register one image to another, disappear due to motion of the ultrasound probe.
Accordingly, what is needed is a system and method for registering multiple ultrasound images into a single 3D image space, without the expense and complication of additional control/measurement hardware, and which addresses the problem of out of plane motion.